The present invention relates generally to the art of welding power supplies. More specifically, it relates to a welding power supply that receives an ac input and provides a welding output.
There are many known types of welding power supplies used for many known types of welding applications. Some welding applications are performed using welding power supplies that are able to be plugged into a typical 115 volt duplex outlet, such as those found in homes, offices, businesses, etc. Such an input is frequently limited to 15 A (sometimes 20 amps) by a circuit breaker that often serves other outlets as well. Accordingly, the power that may be obtained from such an outlet is limited. This limits the power that may be provided to the weld.
Known welding power supplies powered by 115 volt ac utility power includes power supplies having tapped transformers to control the output. Another type uses a transformer with a phase controlled output. Welding is typically performed at up to 20-25 volts, and lesser voltages may result in difficulty welding. Thus, transformer based welding power supplies having an input of 115 volt ac must have a turns ratio that steps the voltage down by no more than a factor of five or six in order to provide adequate welding voltage. This means that, for a 15 A breaker, the maximum welding current would be about 75-90 A. This is inadequate for many welding applications, which may require, for example 100 A or 150 A. However, increasing the current requires a greater turns ratio, which results in the voltage being inadequate. Thus, prior art welding power supplies have provided inadequate current, inadequate voltage, or both.
Other known 115 volt welding systems use inverter or converter type power circuits. However, these power supplies are also necessarily limited by the input power of the duplex outlet. A DC bus created by such a power supply must be at the 20-25 volts needed for welding. The limited input power available again limits output current to an average of about 75-90 A.
Some ac prior art welders provided an unbalanced output to offset the naturally occurring unbalanced load when using a tungsten electrode. A dc bias was provided to add to the load in the EN half-cycle to effectively make the load equal to the EP half-cycle load. The dc offset was provided using a battery and diodes in some systems. However, the battery reduced the output voltage rather than enhanced it. For example, if the EP arc was 28 volts, and the EN arc is 16 volts, a 12 volt battery added to the EN arc (with bypass diodes for EP) would make the effective EN load 28 volts (16 volts from the arc plus 12 volts from the battery). This reduces the current available from the source for a given input power.
Another type of known welding power supply uses battery power as an input. These power supplies are generally limited in their ability to provide power and the duration for which they may provide power.
Because these known power supplies often provide inadequate power due to limitations of the input power, a welding power supply that can provide sufficient power for welding, while having a typical 115 volt duplex input, is desirable. Preferably, such a power supply will provide an output voltage in the range of 20-25 volts and up to 150 amps so that the welding process may be easily performed.
According to a first aspect of the invention a welding-type power supply or method for providing welding-type power to a load includes a transformer with a primary winding and an output secondary winding. The ac side of a rectifier circuit is connected to the output secondary. A battery or other energy storage device, such as a capacitor, is connected in series with the dc side of the rectifier. The series combination is disposed to be connected to the load.
According to a second aspect of the invention a welding-type power supply and a method of providing welding-type power to a load includes an input circuit that receives a 115 volt ac input. A transformer is connected to the input circuit and has a primary to secondary turns ratio of at least about 9:1. An output circuit is connected to the secondary winding.
According to a third aspect of the invention a welding-type power supply and a method of providing welding-type power to a load includes a converting circuit that receives an ac input and provides a dc signal. A battery or other energy storage device, such as a capacitor, is connected in series with the dc signal, and the series combination is connected to the load.
The output secondary winding includes a plurality of taps selected by an output select switch that selectively connects the ac side to one of the taps in one embodiment.
The transformer includes a charging secondary winding, and a charging rectifier causes the battery or energy storage device to be selectively charged in another alternative. The charging may be done in response to a trigger signal from a welding torch, and the connections are made with switches, such as a relay, in various embodiments.
The welding-type power supply is connected to power using a power cord with a male 115 volt plug in other embodiments.
The transformer has a primary to output secondary turns ratio of at least about 9:1 or about 10:1 in various embodiments.
The welding-type power supply can provide a welding current of 150 amps and/or the battery is a 12 volt battery in additional embodiments.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.